THE GRASSHOPPER MICE—HOLLISTER. 



431 



Geographic distribution. — Western North America, from the Great 

 Plains of Alberta, Saskatchewan, and Manitoba south to central 

 Mexico (Aguas Calientes and San Luis Potosi); east to western 

 Minnesota and eastern Kansas. Absent from large areas in the 

 higher Rockies and the Pacific Coast region. (See fig. 1.) 



Rermr'ks.—Onychomys differs from Peromyscus, its nearest generic 

 relative, in its *more hypsodont molars, and in the position and shape 

 of the front cusp of m\ which is distinctly in the outer row of cusps, 

 more coniform, less broadened transversly, and with the unworn 



Fig. 1. Distribution of the Genus Onychomts. 



summit less inclined to division into cusplets; m^ is more reduced; 

 and the coronoid process is greatly lengthened. Although it exter- 

 nally resembles Oricetulus much more than it does Peromyscus, it is 

 as shown by a study of the teeth, separated from the old-world genus 

 by both Peromyscus and Baiomys. The latter, with its close approach 

 to the six-tuberculate pattern in m^, appears, of the thi^ee groups, the 

 nearest to Gricetulus. Osgood ^ has poinfed out certain peculiari- 

 ties of resemblance between the subgenus Podomys, of Peromyscus, 

 and Onychomys; and has suggested the possibility that Podomys is 

 an intermediate form between Onychomys and typical Peromyscus. 

 The reduction in the number of plantar tubercles in Podomys is prob- 

 ably of no importance in this connection, but the higher-crowned 

 teeth and the relative position of the anterior cusp of the first molar 



« North Amer. Fauna, No. 28, p. 227. Apr. 17, 1909. 



